A wireless multi-carrier communication system includes at least one wireless multi-carrier access point and a plurality of wireless multi-carrier communication devices. Advanced wireless multi-carrier communication systems such as the IEEE 802.16e system utilize Adaptive Modulation and Coding (AMC) to improve system performance. With AMC, the modulation and coding scheme (MCS) of a transmitted data stream for a particular receiver is changed to predominantly match a current received signal quality (at the receiver) for the particular frame being transmitted. The modulation and coding scheme may change on a frame-by-frame basis in order to track the channel quality variations that occur in mobile communication systems.
The performance of any system employing AMC is highly dependent upon the accuracy in determining a receiver's channel quality, and in particular the accuracy of the underlying link error probability prediction. Link error probability prediction (LEP) maps the current radio conditions (channel quality) to an expected link performance metric, such as Frame Error Rate (FER). Bad link prediction severely degrades the performance of AMC. In order to achieve high system throughput, a simple link error probability predictor that accurately models coded orthogonal frequency division multiplexing (OFDM) performance or any other multi-carrier modulation is therefore critical for any multicarrier system employing AMC.
Several LEP methods are available, such as the Exponential Effective SIR Mapping method (exp-ESM). Another known method proposes that a wireless multi-carrier communication device advertises a preferred modulation and coding scheme (MCS), and that transmission of data takes place, based on the advertised MCS. The advertised MCS method is considered as an LEP method since advertising an MCS is one way of signaling the link quality. LEPs can vastly differ in terms of performance, complexity, or range of applicability. A simple LEP method may do very well for single antenna transmission case and low coding rate, but may have a severely degraded performance for multiple antenna transmissions where a more complex method could perform very well. Also, LEP methods require a different amount of feedback, for example, SNR based LEP requires very little feedback whereas more advanced LEP methods require more feedback. Depending on the system configuration, the wireless multi-carrier system may or may not tolerate a large amount of feedback.
Known methods for link adaptation do not define a detailed procedure for selecting an LEP method. Moreover, the link adaptation methods are generally designed for one specific LEP method, and are therefore not capable of handling various LEP methods, as conditions change. Therefore, a need exists for a method and system for link adaptation in a wireless multi-carrier system capable of dynamically changing the underlying LEP method, upon which the AMC algorithm relies.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.